1. Field of the Invention
The present invention relates to a diagnostic electrode to be used to supply reference signals to an analyzer circuit. More specifically, the diagnostic electrode includes an active signal generating circuit which creates reference signals to be received and analyzed by the analyzer circuitry.
2. Related Art
It is known to provide an analyzer that includes circuitry for receiving input data related to a test sample and determining characteristics of that test sample based on that data. It is also known to provide a sample holding device to be in contact with the analyzer and thus transmit input information to the analyzer circuitry.
An example of such an analyzer circuitry is described in U.S. patent application Ser. No. 07/750,534 filed Aug. 27, 1991. An example of a known analyzer utilizing such analyzer-circuitry is the STAT-K ANALYZER, (a trademarked product of Porton Diagnostics Inc.), which is described in U.S. patent application Ser. No. 07/763,696 filed Sep. 23, 1991. The disclosures of these two patent applications are hereby incorporated by reference. An example of a sample holding device is disclosed in U.S. patent application Ser. No. 07/401,786, filed Sep. 1, 1989, directed to a disposable sensor.
The STAT-K ANALYZER is constructed so that a disposable sensor can be inserted into a receiving portion of the analyzer. The disposable sensor is designed to receive a sample of the material to be analyzed, and the interface between the sensor and the analyzer conveys information about the sample from the sensor to the analyzer circuitry. That circuitry then interprets that information to determine characteristics of the sample. The analyzer and associated sensor electrode are generally employed for medical purposes and analyze a material, such as blood, by studying the ion content of the material.
The disposable sensor is precalibrated and thus has an initial known ion concentration. When the sample is placed on a receiving region of the disposable sensor, the ions in the sample interact and/or pass through an ion selective membrane of the sensor so as to create an ion imbalance representative of a change in ion concentration. The analyzer circuit detects the ion imbalance and then determines the ion concentration in the sample disposed on the sensor.
In a preferred embodiment the disposable sensor is used only once, i.e., the sensor is used to analyze only one sample and then the user of the analyzer circuit discards the sensor.
The accuracy of any analytical device, especially those used for medical purposes, is most important to the user and must be checked at regular intervals. It is common to provide a daily check of the accuracy of an analytical device as part of a regular quality control routine. Where, as here, the analytical system includes an analyzer and a removable or disposable sensor, inaccuracies in performance can arise from at least three different circumstances. First, inaccuracy can be the result of a failure of the sensor. Inaccuracy can also be the result of a failure in the analyzer. Finally, inaccuracy can be the result of a failure in the interface between the sensor and the analyzer. Typically, when inaccurate results are detected, it is necessary to attempt to isolate the failure in one of these three areas. One possible method for checking the accuracy of the system is to separate the sensor and the analyzer which together have produced the faulty result and separately test the sensor with a different analyzer while testing the analyzer with a different sensor.
There are shortcomings with this evaluation procedure, especially where one of the components, e.g., the sensor, can only be used once. In a two component system it is conceivable that a second sensor will not be more accurate than the sensor involved in the failure. In fact, since single-use sensors may be produced in batches, it is possible that each sensor in the same batch as the sensor involved in the failure will have the same or similar defect. Where batch sizes are large, it may happen that many, if not all, of the sensors available to a given user are from the same batch and thus, all of the sensors in the possession of the user may have the same defect.
Thus, where an analyzer employs a single-use detector module and results have been found to be inaccurate, a conventional problem arises in making an early decision whether to obtain a new batch of the sensors and/or to call expert service for remedial work on the analyzer.
It is known from U.S. Pat. No. 4,882,544 to Uekusa to supply an inspection device for an analyzer for ionic activity. Uekusa provides a passive resistive device as an inspection device. The inspection device has outer dimensions approximately equal to the outer dimensions of a sample measuring device. However, before the analyzer can detect any signals from the inspection device so that the operational capabilities of the analyzer circuitry can be evaluated, the possibly faulty analyzer circuitry itself must supply signals to the passive inspection device. Thus, the reference signal used to test the analyzer circuitry is dependent on the analyzer. This can result in a skewed analysis of the functional capabilities of the analyzer.